1. Field of the Invention
The present invention relates to a heating roller and an image fixing apparatus using the same. More particularly, the present invention relates to a heating roller for preventing slipping of internal structures during the rotation of the roller and an image fixing apparatus using the same.
2. Description of the Related Art
Generally, electrophotographic equipment, such as a copier, a fax machine, and a laser beam printer, is provided with a fixing unit for fixing a toner image that is formed on a recoding medium by an image forming unit at a high temperature and a high pressure. The fixing unit includes a heating roller for generating a high-temperature of heat, and a pressing roller rotating in contact with the heating roller while pressing the heating roller at a predetermined pressure.
Typically, the heating roller has a built-in heater (or heat source), such as a halogen lamp, disposed inside a metal tube, and fixes an image by electric heat from the inside. In this case, however, because the heat source and the surface of the roller are separated from each other, a great loss in heat occurs during the heat transfer process, which results in high power consumption of the heat source.
As an attempt to solve the above-described problem, an improved fixing roller has been developed in recent years. The new fixing roller has an electric resistance heating layer formed near the surface of the roller in which the electric resistance heating layer is used as a heat source for the performance of the fixing roller.
FIG. 1 is a cross-sectional view illustrating the configuration of a conventional heating roller used in a fixing unit for an image forming device.
Referring to FIG. 1, a heating roller 10 includes an exterior pipe 11, a heating coil 12, inner and outer insulating layers 13 and 14, and an interior pipe 15.
The heating coil 12 electrically heats a developed image on the recording medium, and a resistance heating coil is typically used. The heating coil 12 receives power through terminals 16 formed on both ends of the exterior pipe 11.
The exterior pipe 11 is made of aluminum with excellent heat conductibility. As shown in FIG. 1, the exterior pipe 11 is coated with a Teflon coating layer 17 to prevent toner particles from sticking to the surface of the same.
The inner and outer insulating layers 13 and 14 block the migration of an electric current from the heating coil 12 to the surface of the exterior pipe 11 to protect a user from any damages. A layer of mica is widely used as the insulating layer.
The interior pipe 15 is also made of aluminum with excellent heat conductibility. The interior pipe 15 is a means for closely adhering internal structures S, namely, the heating coil 12 and the inner and outer insulating layers 13 and 14 to the exterior pipe 11, and has a predetermined degree of expandability. The interior pipe 15 improves the heat transfer efficiency by ensuring that there is no air gap between the exterior pipe 11 and the internal structures S, so heat from the heating coil 12 is not lost but is fully transferred to the exterior pipe 11. Moreover, the expandability of the interior pipe 15 prevents the internal structures S from slipping from the exterior pipe 11.
However, the expandability of the interior pipe 15 is weakened due to the repetitive thermal expansion of the heating coil. Thus, the internal structures S slip more easily from the exterior pipe 11.
When the internal structures S slip, the heating coil 12 twists because both ends thereof are fixed. In some cases the heating coil is cut off, thereby causing a spark or low heat error.
Accordingly, a need exists for an image fixing apparatus having an improved fixing unit in which elements disposed within a heating roller are substantially prevented from slipping.